My simple goal was to compress PNG files with the following code:
$image = imagecreatefrompng("test.png");
imagepng($image, "result.png", 9, PNG_ALL_FILTERS);
I've also tried with zero and default compression, with the same results.
Original file is like this:
But the result on some (not all) images was like this:
The only way, I can produce good results is with this additional code:
imagealphablending($image, false);
imagesavealpha($image, true);
Why does this simple image manipulation produce this kind of artefacts? And by saving full alpha information, do I get into troubles with some browsers or unneeded filesize?
Is there any other foolproof solution, which would losslessly compress png files?
Related
I'm trying to write a PHP function to convert an SVG image without any antialiasing (so that the final PNG is blocky and contains only the colours specified in the SVG).
The command line equivalent is:
convert +antialias /path/to.svg /path/to.png
I'm assuming that I need to use PHP's Imagick::setOption method to pass in "+antialias", but the documentation is very sparse.
The following snippet will write a PNG file, but none of the options prevents antialiased pixels being rendered:
$image = new Imagick();
// None of these have any affect - output image is always antialiased.
$image->setOption('+antialias', true);
$image->setOption('-antialias', true);
$image->setOption('+antialias', 'true');
$image->setOption('-antialias', 'true');
$image->setOption('antialias', true);
$image->setOption('antialias', false);
$image->setOption('antialias', 'true');
$image->setOption('antialias', 'false');
$image->readImage('/path/to.svg');
$image->writeImage('/path/to.png');
Any help would be great, thanks.
That is not a good way to anti-alias a vector file such as SVG. The proper way in command line would be to set the desired density before reading the file and then resize back to compensate for a large magnification when using a large density. So for example
convert -density 288 image.svg -resize 25% image.png
Nominal density (default) is 72. So 288 = 72*4. Thus we resize afterwards by 1/4 = 25%, unless you want a larger output. Then resize by a larger value.
In PHP Imagick, you can create a new Imagick() instance. Then set the desired density. Then read the input SVG. Then resize. Then set the PNG format and save to disk. See setImageResolution for setting the density in Imagick. See https://www.php.net/manual/en/imagick.setimageresolution.php
I don't think what you want is possible, unfortunately. ImageMagick shells out to Inkscape to render SVGs, and Inkscape has no command-line option to disable antialiasing.
https://graphicdesign.stackexchange.com/questions/138075/export-svg-without-anti-aliasing-in-inkscape-1-0-by-command-line
You could render at high resolution and then do nearest-neighbour downsampling. It would reduce the visible antialiasing, but you would still get some colours not in the SVG file.
I have an eps. I want to make an jpg out of it. I tried everything, but the quality is too bad.
I think imagick takes the original size of the file, makes an jpg, and then makes it bigger without any compression. The problem is, the generated image of the eps is in bad quality, and the bigger image is totally bad.
Here are some configurations I tried:
$imagick = new \Imagick();
$imagick->readImage($imagePath);
$imagick->flattenImages();
$imagick->resizeImage(1024, 0, \Imagick::FILTER_LANCZOS, 1);
$imagick->setImageResolution(300, 300);
$imagick->setImageCompressionQuality(100);
$imagick->setImageCompression(\Imagick::COMPRESSION_JPEG);
$imagick->setCompressionQuality(100);
$imagick->setImageFormat('jpeg');
$imagick->writeImage($new_imagePath);
Can anyone help me with this? I don't get it.
You'll need to set the image density/resolution before you read the Encapsulated PostScript file.
$imagick = new \Imagick();
$imagick->setResolution(100); // or 300
$imagick->readImage($imagePath);
Also note that, by nature, EPS is a vector format, and JPEG is a lossy raster format. Rendering at a low dpi, and resizing up to a given size will always result in poor quality. Either render at a high-dpi & downsample to a given size, or render at expected size & omit any resizing.
I get a QRCode png as base64 from a remote service and need to display it on the web. When blowing the picture up without the "vector" data, it blurs:
I write the base64 to disk with
fwrite($ifp, base64_decode($this->getQRCode()));
The resulting png is a bit small (29x29 pixels). When I open it with e.g. Photoshop, I can blow it up without loss so it looks like the "vector" data is intact. Note the "pixels":
How can I do this on the server side before writing it down to disk and linking to it from the web.
You don't say how you are "blowing the picture up." Have you tried rescaling the image in PHP?
$image = imagecreatefrompng($filename);
$bigimage = imagescale($image, 128, 128, IMG_NEAREST_NEIGHBOUR);
header("Content-Type: image/png");
//dumps directly to output
imagepng($bigimage, null, 0);
Edit: you can try various interpolation modes as specified here, if IMG_NEAREST_NEIGHBOUR isn't suitable. (Also, note the British/Canadian spelling of neighbour.)
The old school way of blowing up images was to (ideally) double pixels. Smoothing the rough edges that were the result of that process was invented later. So now I go with this:
imagescale($image, 128, 128, IMG_NEAREST_NEIGHBOUR);
I have pieced together a PHP class to perform various image related functions using GD functions of PHP.
It works great for all image types. Rotate, flip, resize, crop and to a lesser extent, watermark.
All but the latter work perfectly. For example after a few changes, rotated PNG images retained their transparency whereas before they were losing that and the background turning black. Common problem, it appears. But all working now.
Where I'm still getting stuck is watermarking a PNG image with another PNG image. It appears to work fine with JPG and other images. This is the code (simplified):
public function writeWatermarkSimple()
{
$watermarkFile = 'watermark.png';
$watermarkImage = imagecreatefrompng($watermarkFile);
imagealphablending($watermarkImage, false);
imagesavealpha($watermarkImage, true);
$imageFile = 'image.png';
$baseImage = imagecreatefrompng($imageFile);
imagealphablending($baseImage, false);
imagesavealpha($baseImage, true);
$marginH = imagesx($baseImage) - imagesx($watermarkImage);
$marginV = imagesy($baseImage) - imagesy($watermarkImage);
$cut = imagecreatetruecolor(imagesx($watermarkImage), imagesy($watermarkImage));
imagecopy($cut, $baseImage, 0, 0, $marginH, $marginV, imagesx($watermarkImage), imagesy($watermarkImage));
imagecopy($cut, $watermarkImage, 0, 0, 0, 0, imagesx($watermarkImage), imagesy($watermarkImage));
imagecopymerge($baseImage, $cut, $marginH, $marginV, 0, 0, imagesx($watermarkImage), imagesy($watermarkImage), 80);
if (!imagepng($baseImage, 'watermarked_image.png'))
{
return false;
}
return true;
}
This has been pieced together with various guides and advice people have given based on a similar issue. Again, working perfectly with JPG images and PNG watermarks, but not PNG & PNG.
Some example images:
http://i.imgur.com/hHRWinj.png - This is the watermark I'm using.
http://i.imgur.com/6sy8Ncs.png - This is the image I'm applying the watermark to.
http://i.imgur.com/ghovYLm.png - This is the end result.
The bit I find interesting is that any part of the watermark that is overlaid on a non-transparent portion of the image is working fine. Just the rest of it has the black background.
This leads me to believe I'm close, and I hope that the expertise of you fine people may lead me to the solution.
Thanks ever so for reading.
So, I'm not giving up on finding the correct answer to do this using GD. However, I was overjoyed to find that what needed up to 30 lines of code with GD can be achieved using much less with ImageMagick:
$image = new Imagick();
$image->readimage($this->_image);
$watermark = new Imagick();
$watermark->readimage($this->_watermark->_getImage());
$watermark->evaluateImage(Imagick::EVALUATE_DIVIDE, 2, Imagick::CHANNEL_ALPHA);
$image->compositeImage($watermark, imagick::COMPOSITE_OVER, $marginH, $marginV);
So this is before (with GD):
http://i.imgur.com/AlS0TcO.png
And after (with ImageMagick and the code above):
http://i.imgur.com/zBxlC3R.png
If anyone has an answer that is purely GD then I'd be immensely grateful.
Ran into some similar issues recently and while this may not exactly solve your problem, these were some useful discoveries that I made.
In my case, I have an original .jpg image and a watermark .png image. The watermark image has a fully transparent background. I wanted to specify the opacity in my script and have it change the watermark opacity before placing it on top of the origina image. Most posts out there regarding PHP watermarking assume that the original watermark .png file already has the solid watermark portion set to the correct opacity rather than changing it via the script.
gd didn't like a 24 bit .png and caused some goofy issues. Switching to 8 bit resolved that with gd. On the other hand, imagick works very well with a 24 bit .png and the final result seems to be better.
For me, using gd worked just fine if I was opening the original watermark .png and using imagecopymerge() to set the watermark transparency. If however I tried to scale the original watermark .png (which has transparent background) first, then I would get similar results as you with black or white background portion of where watermark image is. See How do I resize pngs with transparency in PHP? for a partial solution by filling the new wm image with transparent rectangle first. For me this still produced an opaque white background on the final result no matter what I tried.
I switched to imagick and was using setImageOpacity() to change the transparency of my watermark .png before applying it on top of my original image and I was still getting the same effect with a black background. Finally read in the PHP doc for setImageOpacity() that if the original .png has any transparent pixels and you try to lower the opacity, those pixels become opaque (black) with the new transparency applied. Instead, need to use the evaluateImage() function. This will instead evaluate each pixel's alpha channel only and divide by the specifid number.
I assume the black / white background issue with gd is likely due to similar ways that it treats alpha channels when scaling / combining as compared to imagick and if you want to do it all in gd you just need to find some similar way to evaluate and manipulate the alpha channel per-pixel because the "easy" ways seem to take an already transparent background and make it opaque.
So, the solution:
Assuming you want to apply your watermark at an opacity of 45% and you're using imagick, then instead of this:
$watermark->setImageOpacity(.45);
do this
$watermark->evaluateImage(Imagick::EVALUATE_DIVIDE, (1/.45), Imagick::CHANNEL_ALPHA);
You need to divide 1 by your opacity to get the demoninator by which the function will divide the alpha channel value for each pixel. In this case, 1/.45 = 2.2222, so then the function will divide the alpha channel of each pixel by 2.2222. This means a solid pixel (alpha of 1) would result in 1/2.2222 or .45 alpha or transparency when finished. Any pixels that were already transparent (alpha 0) would stay transparent because 0 divided by anything is always what? Zero!
After you change the watermark transparency then you can use compositeImage() to merge the watermark onto the original image.
$im = ImageCreateFromString(file_get_contents($source_file));
ImageFilter($im, IMG_FILTER_GRAYSCALE);
any idea what i could do, to properly grayscale gifs and pngs with transperancy? This snippet actually works good, it transforms jpgs and pngs to grayscale. However gifs are a little bit "buggy" - they don't always work, it depends on the image. Sometimes there are a few pale colors left in them. Moreover this snippet doesn't work with alpha-channels. If i convert a gif or a png with transparancy the transparent parts always get blackened.
Of course im querying the image-type and after "grayscaling" it, i'll set the proper type again.
Have you any ideas?
This code should preserve the alpha, but it's slower than imagefilter:
$im = ImageCreateFromString(file_get_contents($source_file));
$width=imagesx();
$height=imagesy();
for($x=0;$x<$width;$x++)
for($y=0;$y<$height;$y++)
{
$rgb=imagecolorsforindex($im,imagecolorat($im,$x,$y));
$average=ceil(($rgb["red"]+$rgb["green"]+$rgb["blue"])/3);
imagesetpixel($im,$x,$y,imagecolorallocatealpha($im,$average,$average,$average,$rgb['alpha']));
}
If you still have problems try to write this after the image creation (before the $width=..):
imagesavealpha($im,true);
For pngs a simple call to imagesavealpha() solves the problem of black pixels on the alpha channel, complete code:
$im = ImageCreateFromString(file_get_contents($source))
imagefilter($im, IMG_FILTER_GRAYSCALE);
imagesavealpha($im,true);
imagepng( $im, $output );